It has been hypothesized that oxidative stress is involved in the pathogenesis of insulin resistance associated with obesity. Circulating uric acid (UA) is the body's major endogenous plasma antioxidant. Therefore, the investigators evaluated whether alterations in serum UA concentration affect: 1) systemic and skeletal muscle oxidative stress, 2) total antioxidant capacity, and 4) skeletal muscle insulin sensitivity during a hyperinsulinemic-euglycemic clamp.